title: Kinesin-3 is an organelle motor in the squid giant axon.
abstract: Conventional kinesin (Kinesin-1), the founding member of the kinesin family, was discovered in the squid giant axon, where it is thought to move organelles on microtubules. In this study, we identify a second squid kinesin by searching an expressed sequence tag database derived from the ganglia that give rise to the axon. The full-length open reading frame encodes a 1753 amino acid sequence that classifies this protein as a Kinesin-3. Immunoblots demonstrate that this kinesin, unlike Kinesin-1, is highly enriched in chaotropically stripped axoplasmic organelles, and immunogold electron microscopy (EM) demonstrates that Kinesin-3 is tightly bound to the surfaces of these organelles. Video microscopy shows that movements of purified organelles on microtubules are blocked, but organelles remain attached, in the presence Kinesin-3 antibody. Immunogold EM of axoplasmic spreads with antibody to Kinesin-3 decorates discrete sites on many, but not all, free organelles and localizes Kinesin-3 to organelle/microtubule interfaces. In contrast, label for Kinesin-1 decorates microtubules but not organelles. The presence of Kinesin-3 on purified organelles, the ability of an antibody to block their movements along microtubules, the tight association of Kinesin-3 with motile organelles and its distribution at the interface between native organelles and microtubules suggest that Kinesin-3 is a dominant motor in the axon for unidirectional movement of organelles along microtubules.
authors.affiliation: Laboratory of Neurobiology, NINDS, National Institutes of Health, Building 49, Room 3A60, 49 Convent Drive, Bethesda, MD 20892, USA.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: DeGiorgis
authors.forename: Tatyana A
authors.initials: TA
authors.lastname: Petukhova
authors.forename: Teresa A
authors.initials: TA
authors.lastname: Evans
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Reese
mesh_terms: D000818:Animals; D001369:Axons; D049832:Decapodiformes; D016547:Kinesins / Q000502:physiology*; D008854:Microscopy, Electron; D015388:Organelles / Q000502:physiology*; D013045:Species Specificity
chemical_list: D016547:Kinesins